The non-binding proposal is expected to go before shareholders at Apple's annual meeting later this month.

ISS' intervention is significant, as institutional investors in major companies rely on it to guide them on how to vote on shareholder proposals. It played a particularly prominent role in the drawn out proxy fight around HP's proposal to take over Compaq almost ten years ago.

Apple has consistently opposed the idea of making its succession plans public. On the one hand this is understandable, as it would expose its strategic plans and single out its most valued execs making them vulnerable to poaching from rivals. But on the other hand, given Jobs' almost messianic status within and outside the firm, major shareholders are getting nervous about who would lead the company should his absence become permanent.

A spokeswoman for the union told the Financial Times that it wasn't asking Apple to name the potential successors, but rather to simply outline what the succession plan was.

She added that it didn't actually expect the proposal to pass - at least not this year. ®